1. Field of the Invention
This invention relates to an axial flow, elastic fluid turbine apparatus and in particular, to an improved rotating blade structure for the last rotating blade row in the turbine apparatus.
2. Description of the Prior Art
In the prior art, repair of damaged rotating blades in the last rotating blade row in an axial flow, elastic fluid, turbine apparatus is a time consuming and expensive process. The cost emanates not only from the requirement that a portion of the turbine casing first be removed in order to remove the damaged blade, but also from the necessary shut-down time period during which the turbine apparatus is inoperative.
The necessity of opening the turbine casing, and the overall plant shut-down incident thereto, results primarily from the fact that no efficient turbine blade structure which facilitates removal of the damaged blades from the last rotating blade row without dismantling the casing is known to the prior art.
In the prior art, each rotating blade is usually comprised of a curved root portion connected to a platform portion having an air foil portion extending radially outward therefrom.
The platform has a convex arcuate surface and a concave arcuate surface thereon. Both the convex arcuate surface and the concave arcuate surface of the platform portion of the rotating blades have an equal radius. The blades, when disposed a predetermined circumferential distance from each other on the rotor shaft, interfere with each other to prohibit any axial movement of one blade with respect to the other.
Axial movement of blades in the last rotating blade row in the direction of the axial flow of steam, that is, toward the turbine exhaust, is prohibited by interference which occurs between the convex arcuate surface of the platform of one rotating blade abutting against the concave arcuate surface of an adjacent rotating blade. The interference between adjacent rotating blades occurs at approximately the platform center line. Since provision of the arcuate surfaces of the platform portion of the rotating blades having substantially equal radii prohibited axial movement of one rotating blade relative to another in the direction of the turbine exhaust, removal of damaged rotating blades from the last rotating blade row could only be effectuated by first dismantling a portion of the turbine outer casing, with the attendant shutdown expense and time delay.